1. Field of the Invention
This invention relates generally to the manufacture of metal-insulator-semiconductor devices, and more particularly, to a novel method for preventing excessive grain growth and void formation in the polycrystalline silicon gate so as to obviate acid attack of the underlying thin oxide insulator.
2. Description of the Prior Art
In the manufacture of metal-oxide-semiconductor devices having a thin gate oxide layer and a polycrystalline silicon gate where the metal-to-gate contact occurs in vertical alignment with the thin gate oxide, the yields of good devices have heretofore been inexplicably low. We believe that we have discovered the failure mechanism responsible for these low yields to be as follows: The doping of the polycrystalline silicon layer contributes to excessive grain growth with resultant void formation in the polycrystalline silicon gate. During subsequent processing, hydrofluoric acid seeped through the voids and attacked the thin silicon dioxide insulating layer. The insulating effect of the latter was thereby substantially reduced so as to permit shorting and breakdown of the devices at lower applied voltages.